Conventionally, an electric heater used in a high-temperature heating furnace at 700 degree C. or more, particularly 1,000 degree C. or more, is fixed to the surface of a heat insulating material by a staple or a locking pin so as to enable direct heating of the inside of the furnace.
More specifically, as shown in FIG. 9, in the heating apparatus 90 of the prior art, in order to fix an electric heater 2 on the surface of a heat insulating material, a linear heater 2 is disposed in a meander configuration on the surface of a heat insulating material 1, and then ceramic-made pins 3 are inserted into the heat insulating material 1 at the curved portions, or metal-made staples 5 are inserted into the heat insulating material 1 so as to clip the linear heater 2. In the embodiment of FIG. 9, end parts of the linear heater 2 are connected to electrode terminals 4, and the electrode terminals 4 penetrate a through hole provided in the heat insulating material 1 to communicate with the back side.
Such an electric heater has a problem that deformation or sagging readily occurs at a high temperature other than at the fixed points, or repetition of heating/cooling is likely to cause a drop-off. Further, Such an electric heater has not only a problem that the life is short, but also a problem that pin driving or staple driving imposes a large load on the manufacturing process.
In order to solve this problem, a method of fixing an electric heater by embedding or inserting a part of the electric heater into a heat insulating material of felt-formed fiber has been proposed (Patent Documents 1 and 2).
However, in such a method, the stability of the electric heater is still insufficient, or there is room for improvement in terms of the load on the manufacture thereof.